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DarkSide-20k

Data Acquisition System

CHEP - 21/10/2024

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Maria Adriana Sabia

Sapienza, INFN, TRIUMF

on behalf of the DarkSide-20k Collaboration

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Overview

  • DarkSide-20k as a Dark Matter Experiment and much more
  • Light detection in DS-20k using novel SiPMs
  • How to readout the signals from the SiPMs ? DS-20k data acquisition system
    • Overview of the system
    • The Quadrant: a mockup system for DS-20k data acquisition
  • Conclusions and next steps

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Dual phase Liquid Argon Time Projection Chamber currently under construction at Laboratori Nazionali del Gran Sasso (LNGS)

DarkSide-20k experiment

The Detector

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Cryostat filled with 650t of Atmospheric Argon (AAr) and instrumented with photodetectors to work as an outer veto

Inner Veto: 36t of Liquid Underground Argon within a stainless steel vessel and surrounding the TPC to work as a neutron veto

TPC: 50t of Liquid Underground Argon (20t) fiducial constituting the detector core.

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DarkSide-20k experiment

A Dark Matter search experiment…

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WIMP – nucleus coherent elastic scattering → single nuclear recoil, ROI: [30, 200] keVnr

Energy deposition in LAr produces scintillation photons and free electrons

S1: primary scintillation in LAr (energy information and pulse shape discrimination)

S2: secondary scintillation from electroluminescence of electrons in gas pocket (energy information and position reconstruction)

detected signal

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DS-20k can be sensitive to CEvNS (sub-keV recoil energy) via S2-only analysis.

Expected contribution to Supernova Early Warning System (SNEWS 2.0)

… and much more !

DS-20k as a Supernova detector

Event time resolution is dominated by the electron drift time (maximum drift time ~ 3.5 ms)

JCAP 03 (2021) 043

New J.Phys. 23 (2021) 3

Neutrinos can serve as a prompt alert in case of a Supernova event via CEvNS, Coherent Elastic Neutrino-Nucleus Scattering → sensitive to all neutrino flavors!

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Light detection in DS-20k

Silicon PhotoMultipliers (SiPM

Advantages:

  • High gain at low bias voltage
  • Single photon detection resolution
  • High radiopurity
  • Suitable at cryogenic temperature
  • High Photon Detection Efficiency (PDE)

Single Photon Avalanche PhotoDiodes (SPADs) connected in parallel operated in reverse bias mode

IEEE Trans.Nucl.Sci. 65 (2018)

Uncorrelated Avalanche Noise

- Dark Count Rate (DCR)

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Correlated Avalanche Noise

- Afterpulse (AP)

- Internal Cross talk (CT), Prompt (<< 1 ns) or Delayed (> ns)

- External CT

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The main detection unit is the Photo Detection Unit (PDU), made up of 16 Tiles, in turn composed of 24 cryogenic, low noise and low background SiPMs.

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4 tiles (10 cm2x10 cm2) constitute a readout channel. Large area implies higher noise.

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PDUs assembled in the cleanroom packaging facility Nuova Officina Assergi (NOA) at Laboratori Nazionali del Gran Sasso (LNGS).

SiPM 11.8 x 7.9 mm2

SPAD array with 30 µm pitch

Tile: 24 SiPMs, 4.95 x 4.95 cm2

PDU: 16 Tiles, 20 x 20 cm2

21 m2 optical planes

Light detection in DS-20k

from SiPMs to PDUs

CHANNEL

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How to readout the signals from the SiPMs

DS-20k Data AcQuisition system

FEP1

FEPi

PM

TSP1

TSPj

TSPk

Merger

Waveform acquisition and digitization

Filtering and hit/charge reduction

VX2745 digitizers

Front End Processors

Pool Manager

Time Slice Processors

Data sorting and online reconstruction

SNEWS 2.0

Supernova Early Warning System

Data centers (Italy and international partners)

Detector operating in triggerless mode !

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DarkSide-20k data acquisition

Time Slice concept

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  • Data acquisition divided into time slices
  • A time slice is the complete collection of detector data over a fixed amount of time (with overlap with previous slice)
  • Time Slices are submitted individually to a dedicated processor, TSP (see later)
  • Time Slice Marker (TSM) is injected at the digitizer level

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  • Waveforms from the photosensors are digitized by VME VX2745 CAEN digitizer modules 16 bit, 125MS/s ADC
  • Custom firmware developed at TRIUMF laboratory designed to identify only waveform segments containing a signal
  • Dynamic waveform window: enlarge the gate if the post-trigger contains a new trigger

Waveform digitization

(single PE)

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FEP1

FEPi

  • DS-20k will operate in triggerless mode, with an expected event rate of 200 evts/s → we cannot save all the individual channel waveforms to disk !
  • Filtering is necessary to remove noise spikes (ARMA algorithm)
  • Waveform reduction to hit time/charge (# PEs) is needed in real time (still 2PB/year!)
  • Data are sorted into 1 s time slices to be sent to the next acquisition stage

Front End Processors (FEPs)

The challenge of data reduction

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  • Hits sequences belonging to the same 1 s time slice are gathered into the same online computing node
  • Time slices are sent via raw TCP/IP sockets
  • Perform high level analysis on the TSPs (hit clustering / pulse finding, energy, XY...)
  • TSPs responsible for streaming data according to the physics event

FEP1

FEPi

Time Slice Processors (TSPs)

The challenge of data reduction

TSP1

TSPj

TSPk

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  • The Pool Manager (PM) communicates with both the FEPs and TSPs via ZeroMQ message queue: it gets informed by the FEPs about the available time slices and from TSPs about their status
  • The PM informs the FEPs of the next available TSPs

FEP1

FEPi

Pool Manager (PM)

Orchestrating the data flow

TSP1

TSPj

TSPk

PM

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  • Time slices from different TSPs are collected into the Merger, stored to disk and sent to Data Centers
  • The Merger can also perform physics analysis on longer timescales like Supernova identification and send the results to the Supernova Early Warning System (SNEWS 2.0)

FEP1

FEPi

The Merger

TSP1

TSPj

TSPk

PM

Merger

SNEWS 2.0

Data centers (Italy and international partners)

Supernova Early Warning System

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GDM

Global Data Manager (GDM) and Crate Data Manager (CDM)

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CDM

CDM

Transmits to 12 VX:

  • Common clock
  • VX commands

Collects up to 12 VX:

  • Module busy bits
  • Prompt “self-trigger “ bits

GDM

CDM

4x3 optical links to CDM

Ethernet link

I/Os

link to GDM

6x2 links to VX2745

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The Quadrant

A test bench for DS-20k data acquisition

  • ¼ of DarkSide-20k data acquisition system up and running at TRIUMF laboratory (Vancouver, Canada)
  • System structure:
    • 1 x GDM
    • 1 x CDM
    • 12 x VX2745 digitizers
    • 6 x FEP computers
    • 1 x 48 ports 10 GbE switch

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  • The system allows for firmware testing, digitizer software and machine-specific softwares performing the online analysis

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A software implementation of the full data flow

Input can be real data from the VX2745 or binary data with simulated waveforms

DAQ infrastructure built in MIDAS (Maximum Integrated Data Acquisition System) software package developed at TRIUMF and PSI

Monitoring system under development: key quantities displayed on a webpage

A mockup of DS-20k

data flow

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Conclusion and next steps

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A lot of results…

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  • DAQ quadrant system operational at TRIUMF
  • System expected to be shipped to Laboratori Nazionali del Gran Sasso in Feb/March 2025
  • Paper on DarkSide-20k DAQ in preparation for publication in late 2025

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… and a lot more to come!

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  • Monitoring system to be completed with additional features
  • Online analysis to be refined and tested
  • Supernova trigger to be implemented
  • DAQ chain and online analysis to be tested with data from DS-20k prototype, currently running at Università Federico II, Naples.

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THANK YOU FOR YOUR ATTENTION!

Maria Adriana Sabia

mariaadriana.sabia@uniroma1.it

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Backup

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64 channels/module merged in the same buffer where they are sorted in time

“Ladder” trend expected due to time sorting

The Tx to the sorting is 64 bits per 4 ns = 8x faster than the readout

The readout is 16 bits per 8 ns

Time sorting + merging buffer

ch0

ch63

BUSY logic

Firmware implementation

= Input

= Transmission (Tx) output FIFO to sorting buffer

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Software for the DAQ

BUSY logic simulation: the challenge

  • Triggerless mode for maximum flexibility …
  • … but event bursts can introduce dead time (DAQ BUSY)!
    • multiple scattering events from gamma radioactivity
    • large pulses
  • Simulation of the digitiser firmware busy logic to evaluate impact on detector exposure

Averaged over the channels in a module

Mean buffer fullness (%)

Trigger rate per channel (Hz)

Preliminary

Buffer occupancy (%)

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BUSY logic�Simulation vs data comparison

  • Same waveform pattern can fed into the digitizers
  • Buffer level of each channel can be read out from the front panel and fed into an oscilloscope
  • The firmware implementation also allows for the most occupied channel buffer to be retrieved

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The merger

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3 groups of monitoring quantities:

  1. per-channel monitoring: event variables such as fingerplots and hit rates, some expensive computations like noise FFTs, manual studies like individual waveforms visualization
  2. detector-level monitoring: S1/S2 identification, energy spectra, pulse-level statistics
  3. DAQ monitoring: transmission rates, buffer sizes, CPU usages

Monitoring system